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            <small>
              <a href="#Procedure">Procedure<br></a>
              <a href="#Abstract">Abstract<br></a>
              <a href="#Required_Reading">Required_Reading<br></a>
              <a href="#Keywords">Keywords<br></a>
              <a href="#Brief_I/O">Brief_I/O<br></a>
              <a href="#Detailed_Input">Detailed_Input<br></a>

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              <td style="vertical-align: top; width: 50%; text-align: center;">
              <small>               <a href="#Detailed_Output">Detailed_Output<br></a>
              <a href="#Parameters">Parameters<br></a>
              <a href="#Exceptions">Exceptions<br></a>
              <a href="#Files">Files<br></a>
              <a href="#Particulars">Particulars<br></a>
              <a href="#Examples">Examples<br></a>

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              <small>               <a href="#Restrictions">Restrictions<br></a>
              <a href="#Literature_References">Literature_References<br></a>
              <a href="#Author_and_Institution">Author_and_Institution<br></a>
              <a href="#Version">Version<br></a>
              <a href="#Index_Entries">Index_Entries<br></a>
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<h4><a name="Procedure">Procedure</a></h4>
<PRE>
   SpiceDouble clight_c ( void )

</PRE>
<h4><a name="Abstract">Abstract</a></h4>
<PRE>
   Return the speed of light in a vacuum (IAU official
   value, in km/sec).
</PRE>
<h4><a name="Required_Reading">Required_Reading</a></h4>
<PRE>
   None.
</PRE>
<h4><a name="Keywords">Keywords</a></h4>
<PRE>
   CONSTANTS


</PRE>
<h4><a name="Brief_I/O">Brief_I/O</a></h4>
<PRE>
   The function returns the speed of light in vacuo (km/sec).
</PRE>
<h4><a name="Detailed_Input">Detailed_Input</a></h4>
<PRE>
   None.
</PRE>
<h4><a name="Detailed_Output">Detailed_Output</a></h4>
<PRE>
   The function returns the IAU official value for the speed of light
   in vacuo: 299792.458 km/sec.
 </PRE>
<h4><a name="Parameters">Parameters</a></h4>
<PRE>
 
   None. 
 </PRE>
<h4><a name="Exceptions">Exceptions</a></h4>
<PRE>
   Error free.
</PRE>
<h4><a name="Files">Files</a></h4>
<PRE>
   None.
</PRE>
<h4><a name="Particulars">Particulars</a></h4>
<PRE>
   The function always returns the constant value shown above.
</PRE>
<h4><a name="Examples">Examples</a></h4>
<PRE>
   The following example uses <b>clight_c</b> to determine the one-way
   light-time (tau) to an object whose position relative to an
   observer is contained in pos.

      tau = <a href="vnorm_c.html">vnorm_c</a> ( pos ) / <b>clight_c</b> ();

   Note that the SPK readers

      <a href="spkezr_c.html">spkezr_c</a> 
      <a href="spkez_c.html">spkez_c</a> 
      <a href="spkpos_c.html">spkpos_c</a> 
      <a href="spkezp_c.html">spkezp_c</a> 

   return the one-way light time as an output, for example

      <a href="spkez_c.html">spkez_c</a>  ( ..., &amp;tau );
</PRE>
<h4><a name="Restrictions">Restrictions</a></h4>
<PRE>
   None.
</PRE>
<h4><a name="Literature_References">Literature_References</a></h4>
<PRE>
   None.
</PRE>
<h4><a name="Author_and_Institution">Author_and_Institution</a></h4>
<PRE>
   N.J. Bachman    (JPL)
   W.L. Taber      (JPL)
   I.M. Underwood  (JPL)
   E.D. Wright     (JPL)
</PRE>
<h4><a name="Version">Version</a></h4>
<PRE>
   -CSPICE Version 1.0.2, 07-FEB-2008 (EDW) (NJB)

      Corrected typos in header titles:
      
      Detailed Input to Detailed_Input
      Detailed Output to Detailed_Output

      Updated example to show pointer output argument
      `tau' and list other high-level SPK routines that
      return light time. Call to bodmat_c was removed
      from example.
      
   -CSPICE Version 1.0.1, 11-NOV-2006 (EDW)

      Added Parameters section header.

   -CSPICE Version 1.0.0, 16-APR-1999 (EDW)
</PRE>
<h4><a name="Index_Entries">Index_Entries</a></h4>
<PRE>
   measured velocity of light in a vacuum
</PRE>
<h4>Link to routine clight_c source file <a href='../../../src/cspice/clight_c.c'>clight_c.c</a> </h4>

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   <pre>Wed Jun  9 13:05:20 2010</pre>

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